1. Field of the Invention
The present invention relates to a liquid crystal display device in which the display gray-scale of a liquid crystal panel can be adjusted, and a liquid crystal driving circuit therefor.
2. Description of the Related Art
A conventional liquid crystal driving circuit inputs display data, generates gray-scale voltages, selects the gray-scale voltage corresponding to the given display data and then outputs the gray-scale voltage thus selected to a liquid crystal panel.
For example, in a liquid crystal driving circuit for outputting 64-gray-scale voltages, 8-gray-scale voltages are generated by resistance-dividing each section between two respectively adjacent reference voltages of 9 levels supplied from an external device, and finally 64-gray-scale voltages in total are generated. The gray-scale voltage corresponding to each display data is selected from the 64-gray-scale voltages thus generated, and output to the liquid crystal panel.
For example, 1994 SID INTERNATIONAL SYMPOSIUM DIGEST of TECHNICAL PAPERS 23:2 (pp. 351-354) discloses a liquid crystal driving circuit for generating and outputting gray-scale voltages on the basis of reference voltages supplied externally.
In this liquid crystal driving circuit, a reference voltage is adjusted to generate and output a gray-scale voltage to a liquid crystal panel having a non-linear brightness vs. applied voltage characteristic as generally shown in FIG. 4 so that the output voltage to the display data is matched with the characteristic of the liquid crystal panel.
However, in the conventional technique, the resistance values of voltage-dividing resistors are fixed, and eight gray-scale voltages generated on the basis of two reference voltage values have a linear relationship. When the gray-scale voltage is near to 1V or 4V, the eight brightness values thus obtained have a non-linear relationship to the gray-scale code as shown in FIG. 4 of the prior art as in the case of transmittance.
Accordingly, it is insufficient to merely adjust the reference voltage in order to adjust the display brightness balance (gray-scale display characteristic) of each gray-scale. Therefore, it has hitherto been difficult to perform xcex3-correction to correct distortion of the gray-scale display characteristic due to an inherent characteristic of a device, and implement a gray-scale display characteristic and a color tone which are matched with a user""s taste or suitable for displaying a target image.
An object of the present invention is to provide a liquid crystal driving circuit and a liquid crystal display device which can adjust the display brightness and the variation characteristic of color to display data values input.
Embodiments of the present invention disclosed in this application will be described briefly as follows.
That is, according to a first aspect of the present invention, there is provided a liquid crystal driving circuit for driving a data line of a liquid crystal panel including the data line and a scan line to apply a voltage to liquid crystal, which is characterized by comprising: a latch address control circuit for successively generating a latch signal to pick up display data; a first holding circuit for picking up and holding the display data of an amount corresponding to an output data line in accordance with the latch signal; a second holding circuit for further picking up and holding the display data, held in the first holding circuit, of the amount corresponding to the output data line in accordance with a horizontal synchronous signal at the same time; a set register for operating setting of a gray-scale voltage value of gray-scale voltage; a gray-scale voltage generating circuit for receiving a plurality of different reference voltages and generating gray-scale voltages whose number is larger than that of the reference voltages in response to an instruction of the set register; a gray-scale voltage selection circuit for selecting the gray-scale voltage in accordance with the display data held in the second holding circuit; and an amplifying circuit for amplifying and outputting the gray-scale voltage selected by the selection circuit.
It is preferable that the gray-scale voltage generating circuit has a plurality of variable resistors whose resistance values can be set by the set register, and difference voltages among a plurality of liquid-crystal power sources are resistance-divided by the variable resistors to generate the gray-scale voltages.
It is preferable that each of the variable resistors includes plural resistors and switches for excluding the corresponding resistance component of the plural resistors in the variable resistor.
It is preferable that the amplifying circuit has an operational amplifier, wherein the operational amplifier includes one or plural variable resistors whose resistance values can be set by the set register, thereby determining an amplification factor.
Further, according to a second aspect of the present invention, there is provided a liquid crystal driving circuit for driving a data line of a liquid crystal panel including the data line and a scan line to apply a voltage to liquid crystal, which is characterized by comprising: a latch address control circuit for successively generating a latch signal to pick up display data; a first holding circuit for picking up and holding the display data of an amount corresponding to an output data line in accordance with the latch signal; a second holding circuit for further picking up and holding the display data, held in the first holding circuit, of the amount corresponding to the output data line in accordance with a horizontal synchronous signal at the same time; a set register for operating setting of a gray-scale voltage value of gray-scale voltage; a gray-scale voltage generating circuit for receiving a plurality of different reference voltages and generating gray-scale voltages whose number is larger than that of the reference voltages in response to an instruction of the set register; a gray-scale voltage selection circuit for selecting the gray-scale voltage in accordance with the display data held in the second holding circuit; and an amplifying circuit for shifting the gray-scale voltage selected in the selection circuit by an offset voltage, amplifying the gray-scale voltage thus shifted with an amplification factor indicated by the set register, and then outputting the gray-scale voltage thus amplified.
It is preferable that the set register for setting the amplification factor of each operational amplifier of the amplifying circuit is provided for each of three colors R(red), G(green) and B(blue), and each set register can set and change the amplification factor for every color.
It is preferable that the offset voltage of the amplifying circuit is generated by resistance-dividing an offset reference voltage and a common voltage with a plurality of variable resistors so that the voltage value of the offset voltage is variable.
It is preferable that the set register is supplied with set register setting data to set the set data with a set data set clock, or is supplied with set value data to generate set data on the basis of a clock signal generated by multiplying a latch signal from a latch address control circuit and a set enable signal.
Still further, according to a third aspect of the present invention, there is provided a liquid crystal display device which is characterized by comprising: the above liquid crystal driving circuit; a liquid crystal panel which includes a data line and a scan line to apply a voltage to liquid crystal; a scan driver for driving the scan line of the liquid crystal panel; a control circuit for setting the gray-scale voltage output from the liquid crystal driving circuit to control the liquid crystal driving circuit and the scan driver; and a reference voltage generating circuit for generating reference voltages for the liquid crystal driving circuit, wherein input display data are converted to a variable gray-scale voltage and displayed on the liquid crystal panel.
Still further, according to a fourth aspect of the present invention, a liquid crystal driving circuit for driving a data line of a liquid crystal panel having the data line and a scan line, is characterized by comprising: a holding circuit for holding display data of an amount corresponding to an output data line; a set register for setting the voltage value of a gray-scale voltage; a gray-scale voltage generating circuit for receiving plural different reference voltages and generating on the basis of an instruction of the set register gray-scale voltages whose number is larger than that of the reference voltages; and a gray-scale voltage selection circuit for selecting a gray-scale voltage in accordance with the display data held in the holding circuit.